JP2004279407A - Fine region analysis method for organic material and its device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for evaluating an organic material in several-namometer order. <P>SOLUTION: The device and the method are provided for evaluating the organic material in several-namometer order, which are not established in conventional technology. In particular, information about energy in a transition process for the organic material between electron levels is obtained with a space resolution of several namometer or less from the direction of the surface or the cross section, and it is also applicable for the evaluation of the interface condition of heterogeneous substances when bonded to each other. For example, the gradient or charged condition of a potential on the interface between an electrode and a organic layer of a semiconductor organic material or an organic luminescent device is evaluated and a band diagram of an element is drawn in accordance with its result, thus actualizing high-degree functional development of the element. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a new analysis method for an organic material (including a device using an organic material), and more particularly, to a local analysis method for analyzing an organic material in units of minute regions on the order of nanometers (10 ⁻⁹ m).
The present invention establishes new analytical methods for organic materials, such as transition energy evaluation, charge state evaluation, and interface evaluation with different materials of organic materials, for example, organic EL materials, and can be used for new application development of organic materials. is there.

  Conventionally, evaluation of characteristics related to molecular orbitals such as optical transition energy of organic materials has been performed by using an ultraviolet-visible spectrophotometer (UV-Vis), an X-ray photoelectron spectrometer (XPS), an ultraviolet photoelectron spectrometer (UPS), and the like. Has been evaluated. These analysis methods are analysis methods in which the analysis area is a micron to submicron area or an area area larger than that, and which is specialized for analyzing the surface state.

On the other hand, in the field of semiconductor analysis, it is necessary to locally measure an impurity concentration distribution and a potential distribution in a minute region inside a semiconductor. For this reason, a microscopic region is analyzed by a semiconductor analyzer having an electron microscope equipped with an electron energy spectrometer (for example, see Patent Document 1).
JP-A-10-241719

  As described above, in the analysis of the characteristics related to the molecular orbital of the organic material which has been conventionally performed, the analysis area is at most a micron to sub-micron area even if the analysis area is small, and the analysis is specialized in the surface state. The amount of information to be obtained was small and the application fields of the analysis results were limited.

In a semiconductor analyzer equipped with an electron microscope equipped with an electron energy spectrometer, the electron beam diameter can be reduced to the order of nanometers, so that the analyzer can analyze every fine region on the order of nanometers. Since it was thought that useful data could not be obtained only by reducing the signal even if the measurement was performed on the order or less, the measurement was not performed in the nano-order region. Further, a sampling technique for measuring an organic material on a nano-order has not been established, and the semiconductor analyzer has not been applied to the analysis of the organic material.
In particular, an organic device in which a plurality of materials including an organic material are laminated has been manufactured. However, since it is difficult to sample a nano-order fine region along the cross-sectional direction, an electron microscope as described above is used. Energy analysis method could not be established.

The present invention is characterized in that an organic material is analyzed on a nano-order by an analysis method that has not been previously conceived.
Further, the present invention provides an analysis method capable of obtaining information on valence electron transition, charge state, potential, and the like in nano-order of an organic material from a surface direction or a cross-sectional direction by devising a sampling method. Aim.

  In particular, it is an object of the present invention to provide an analysis method that enables analysis in a region of 10 nm or less, particularly about several nm or less, and that can evaluate an interface state when a heterogeneous substance including an organic material is bonded. More specifically, for example, an analysis method that can evaluate a potential gradient at an interface between an electrode and an organic layer in a semiconductor organic material or an organic light-emitting device is provided, and a high-level expression of an element is realized, such as creating a band diagram. The purpose is to:

The method for analyzing a fine region of an organic material according to the present invention may be applied to an analysis region having a size similar to or smaller than the size of a single molecule to be analyzed, or an analysis region having a diameter of a circumcircle of 0.01 nm to 10 nm. It is characterized in that at least one of a potential and a charge state of a material is evaluated. “Analytical region with a circumscribed circle having a diameter of 0.01 nm to 10 nm” means that the diameter of a circumscribed circle surrounding the analytical region is approximately 0.01 nm to 10 nm. The shape of the analysis region itself may be any shape such as a circle, an ellipse, and a polygon. The “single molecule size” refers to the diameter of a circumscribed circle surrounding a single molecule.
In the method for analyzing a fine region of an organic material according to the present invention, for example, an electron beam having a beam diameter equal to or smaller than the size of a single molecule of a measurement target molecule, or 0.01 nm to 10 nm is used. , And analyzing the fine region of the organic material based on the electron energy loss data when the electron beam passes through the sample. The shape of the electron beam may be any shape such as a circle, an ellipse, and a polygon. The “beam diameter” refers to the diameter of a circumscribed circle surrounding the electron beam.
In addition, in addition to the above, the method for analyzing a fine region of an organic material according to the present invention may be such that, in the method using an electron beam, an electron microscope equipped with a monochromator for making incident electrons monochromatic is also a method called an energy filter electron microscope. , Can be implemented. In addition to the method using an electron beam, the analysis method of the present invention uses a scanning probe microscope, for example, a scanning tunneling microscope, a conductive atomic force microscope, a scanning potential microscope, a scanning microscope such as a spreading resistance microscope. And XPEEM (X-ray photoelectron microscope).

In addition, a sample containing an organic material is cut into a flake shape under a water-inhibited condition by a FIB or / and a cryo-microtome, and the beam diameter of the cut flake sample is substantially equal to the size of a single molecule of a molecule to be measured. An electron beam having a size smaller than the above or 0.01 nm to 10 nm is incident, and a fine region of the organic material is analyzed based on data on electron energy loss when the electron beam passes through the flake sample. .
According to this, the organic material is cut into slices under water-free conditions, so that the organic material does not react with moisture and the chemical state of the organic material itself, such as the electronic structure, can be analyzed without change. Becomes possible.
After the sample containing the organic material is cut into a flake shape by the FIB, a damaged portion generated on the cut surface may be further cut with a cryomicrotome.
The thickness of the slice when the sample is cut into a slice shape may be 1 nm to 300 nm. According to the present invention, not only a sample having a thickness of several nm but also a sample having a thickness of 10,000 nm or more can be measured.
The sample has a structure in which two or more different materials including an organic material are stacked, and may be cut out in a direction in which the stacked cross section of the sample appears.
The sample may be an organic EL device.
The sample may be an organic semiconductor device.
Data relating to electron energy loss may be acquired by an energy filter type electron microscope device.

The electron energy loss associated with the transition process between π-π ^* electron energy levels, the ionization transition process, etc., related to the molecular orbital of the organic material may be analyzed.
The data relating to the electron energy loss may be electron energy loss data relating to a molecular orbital of an organic material, a transition process between π-π ^* electron energy levels or an ionization transition process.
The analysis performed based on the data regarding electron energy loss may be an analysis of a local charge state or a charge distribution state.
The analysis performed based on the data regarding the electron energy loss may be an analysis of a local potential or a potential distribution of the organic material.
The analysis performed based on the data regarding the electron energy loss may be an analysis of an interface between the organic material and another material adjacent thereto and a characteristic distribution near the interface.
The analysis performed based on the data regarding the electron energy loss may be an analysis of a difference in energy levels involved in transport of electrons or holes in a junction region between different materials including an organic material.

  Further, the organic material fine region analysis apparatus of the present invention includes a sample mounting portion for mounting a sample containing an organic material, and an electron beam for emitting an electron beam having a beam diameter of 0.01 nm to 10 nm to the sample. A beam irradiation mechanism and an electron energy loss detection unit that acquires electron energy loss data when the electron beam passes through the sample are provided.

The analyzer adjusts the acceleration energy of the electron beam in the range of 5 to 1000 keV so that the half width of the energy loss peak caused by the transmission of the electron beam through the sample is in the range of 0.02 eV to 3.0 eV. And a transition energy value corresponding to the sample may be obtained.
A sample heating / cooling mechanism may be further provided.
A molecular orbital method calculation function may be further provided.

According to the present invention, the potential and charge state of an organic material in an analysis region that is about the same as or smaller than the size of a single molecule to be analyzed, or in an analysis region in which the diameter of a circumscribed circle is 0.01 nm to 10 nm. Can be evaluated, and information useful for developing an organic material can be obtained.
When an electron beam is used, an electron beam having a beam diameter of a single molecule or a smaller size, specifically, 0.01 nm to 10 nm is incident on the organic material, and the electron beam is applied to the sample. By analyzing the fine region of the organic material based on the electron energy loss data at the time of transmission, it is possible to obtain new data on the organic material which has not been obtained in the nano order in the past.

  In addition, information on energy of a transition process between electron levels in an organic material can be obtained with a spatial resolution of 1 nm or less from a surface direction or a cross-sectional direction. In particular, it can be applied to the evaluation of the interface state when dissimilar substances are joined.

  It is possible to evaluate a potential gradient at an interface between an electrode and an organic layer in a semiconductor organic material or an organic light emitting device, create a band diagram, and realize a highly advanced function of the element.

Hereinafter, embodiments of the present invention using an electron beam will be described with reference to the drawings.
First, as an apparatus for measuring electron energy loss, an energy filter type electron microscope (EF-TEM) capable of selecting and analyzing specific energy from an incident electron beam will be described.

Energy Filter Type Electron Microscope FIG. 1 is a diagram illustrating a method for measuring electron energy loss using an energy filter type electron microscope. In the figure, reference numeral 1 denotes an accelerated incident electron, which makes it possible to change the acceleration energy of an electron beam depending on an object to be analyzed (the effect of the acceleration energy will be described with reference to FIG. 10). The adjustment of the acceleration energy is performed in the range of 5 to 1000 keV by an adjustment mechanism such as an electromagnetic lens which is provided as a standard feature in the electron microscope. Reference numeral 2 denotes a measurement (observation) sample made of an organic material. The measurement sample may be a single organic material, may contain a plurality of organic materials, or may be configured as a structure such as a device containing the organic material. Reference numeral 3 denotes a temperature control mechanism for heating and cooling the sample under analysis, which enables measurement under various temperature conditions (the effect of heating and cooling will be described in the example of FIG. 11). .

  Reference numeral 4 denotes an analysis region (a region irradiated with an electron beam) in the measurement sample, which has a diameter of 0.01 nm to 10 nm, preferably 0.1 nm to 5 nm (generally the same as the size of a single molecule to be analyzed, Or smaller area). In this analysis region, a focused electron beam probe (probe diameter can be focused to approximately 0.1 to 5 nm) is produced by adjusting excitation of an electrostatic lens such as a condenser lens or an objective lens of an electron microscope, Obtained by irradiating the sample. Normally, when an electron beam having energy is applied to a sample, the diffusion region of the incident electrons in the sample expands according to the type of the constituent elements of the sample, the convergence angle of the probe, the thickness of the sample, and the like.

In particular, focusing on the sample thickness, the theoretical calculation by Monte Carlo simulation shows that when a thin film made of 100% carbon is irradiated with an electron beam probe having a beam diameter of 0 nm at the time of incidence and an acceleration voltage of 100 keV, a film thickness of 50 nm is obtained. When the film thickness is 1.9 nm or 10 nm, the thickness extends to 0.2 nm. In electron beam energy loss (EELS) analysis, only elastic and inelastic scattered electrons transmitted through a sample are used as signals. In order to achieve a spatial resolution of several nanometers or less, a signal from the entire region where electrons are diffused is not obtained.In order to achieve a spatial resolution of several nanometers or less, conditions such as minimizing the beam diameter during analysis and making the sample as thin as possible Need to be satisfied.
Specifically, the beam diameter is preferably approximately the same as or smaller than the size of a single molecule of the molecule to be measured, and specifically, it is preferably 0.01 nm or more and 10 nm or less. Desirably, the sample thickness is 300 nm or less, more preferably 50 nm or less.

Reference numeral 5 denotes a spectroscope such as a magnetic prism that separates an electron beam for each energy. Reference numeral 6 denotes a specific energy lost due to various interactions with a sample (inelastic scattering phenomenon), and transmission transmitted by the spectrometer 5 for each energy. The electron traveling direction, 7 is a detector such as a CCD element for detecting each loss energy of transmitted electrons separated for each energy, and 8 is an electron beam energy loss (EELS) spectrum obtained by the detector.
The electron beam energy loss spectrum 8 can be compared with the molecular orbital method calculation result 9 calculated by a separately known method (described with reference to FIG. 9).

Electron Energy Loss Spectrum Next, acquisition of an electron energy loss (EELS) spectrum by an energy filter type electron microscope (EF-TEM) will be described.
An example in which the incident electron beam 1 gives energy to the sample 2 to excite electrons in the 1s orbit (K shell) of the atoms constituting the sample will be described. In atoms in the ground state, electron levels below the Fermi level are almost entirely occupied by electrons near room temperature (depending on the temperature of the sample), and inner-shell electrons such as 1s orbitals (K-shell) The excited energy level is an unoccupied state level higher than the Fermi level. Therefore, when the incident electron 1 loses energy equal to or greater than the energy difference ΔE between the 1s level and the Fermi level, the probability of excitation of the 1s electron sharply increases, and accordingly, the energy position of ΔE in the EELS spectrum is increased. A sharp peak will appear. The peak appearing in the EELS spectrum with the excitation of the inner shell electrons is particularly called an edge because of its sharp rise.

On the other hand, in an organic material, a transition process between electron energy levels related to molecular orbitals occurs in addition to the transition from the core level of constituent atoms. It has been found that by measuring an organic material with a spatial resolution of several nm or less, the transition process relating to this molecular orbital can be clarified.
That is, by limiting the analysis area 4 to 10 nm or less, and more preferably to 5 nm or less, the analysis area 4 becomes almost equal in size to each molecule, and the macro area obtained by the conventional XPS, UPS, UV-Vis, etc. It was found that, unlike information from the entire molecular assembly from a particular region, information unique to the molecule could be obtained accurately.

  As an analysis example of an organic material using an energy filter type electron microscope (EF-TEM), there has been a report on polyphenylene ether particles dispersed in a polyamide so far. In that case, it is qualitatively reported that the polyphenylene ether particle system has a diameter of 1 to 5 μmφ, and that the energy transition spectrum relating to the molecular orbital is not observed in the polyamide, but is observed in the range of 6 to 8 eV in the polyphenylene ether. Only.

  That is, in the past, for analysis of the energy loss spectrum, if the analysis area was reduced from a micron order to a nano order, the signal was reduced, and it was considered that analysis was difficult or disadvantageous. In the present invention, even when the analysis region is in the nano order, by devising the method of preparing the sample, not only the spatial resolution can be made in the nano order, but also the transition process between electron levels, information on the transition process It was found that the charge state and local potential derived from can be measured.

In addition, it was also found that by comparing each energy loss spectrum with the result of molecular orbital calculation, each spectrum can be quantitatively given meaning.
Furthermore, when the organic material is a thin film, the charge state and local state derived from information on the transition process between the levels and the transition process are evaluated by evaluating the direction parallel to the deposition surface of the organic material layer (cross-sectional direction). It was found that the distribution in the depth direction about the potential could be evaluated.

The method of preparing the measurement sample The sample preparation method used in the present invention is a cutting method typified by a cryomicrotome, a method using an ion beam typified by a focused ion beam (FIB) device, and is prepared under water-free conditions. Things are good. The reason why it is preferable to prepare under water-free conditions is that many of the functional organic materials easily react with moisture, and the property as an electronic material may be deactivated by reacting with moisture. .
The portion other than the organic material is polished using a combination of polishing and ion milling, a method of thinning a sample using an electrochemical reaction represented by an electropolishing method using a chemical substance, and the like (for example, Any method may be used, such as a technique called lift-off, in which a specific layer is etched (for example, SiO ₂ ) using hydrofluoric acid, and the remaining material is analyzed. It may be.

In any case, a thinning method that can measure the original EELS spectrum of the sample with a spatial resolution of several nm or less without damaging the sample as much as possible is desirable.
In particular, a sampling technique for analyzing a transition process related to a molecular orbital from the cross-sectional direction with a spatial resolution of 10 nm or less will be described with reference to FIG. 4 described later.

It is desirable that the thickness of the sample is a measurable thickness (1 nm or more) and is as thin as possible without obtaining an effective signal, and the thickness is 300 nm or less, preferably 50 nm or less.
As another irradiation electron beam condition in acquiring an EELS spectrum, it is necessary to suppress the influence of electron beam irradiation damage when the electron beam passes through the sample. For example electron dose (dose) of the electron beam damage occurs at room temperature, at an accelerating voltage 100keV in polyethylene, a 3.1electrons / Å ^2, in tetracene at an acceleration voltage 100keV, a 100electrons / Å ^2. The electron dose depends not only on the accelerating voltage but also on the sample temperature, measurement time and observation magnification.
As an effect of lowering the sample temperature, the electron beam damage amount of glucose-substituted tRNA is improved by 20.5 times by changing the temperature from room temperature to -265.1 ° C. The effect of cooling the observation sample also produces an effect of accurately analyzing the EELS spectrum (described in detail in FIG. 11). Electron dose to be given to the sample preferably should not exceed 0.1electrons / Å ² at room temperature, so as -196 does not exceed 10electrons / Å ² at ° C., so as not to exceed the 50electrons / Å ² in -250 ° C. Adjust.

  Next, examples of the present invention will be described for each sample state of an organic material and each analysis purpose.

(Evaluation method when the organic material is a powder sample)
First, an evaluation method when the organic material is a powder sample will be described.
As a specific sample, “Alq ₃ ”, which is famous as a light-emitting layer of an organic EL material (Chem. 1)
Was used.

  This powder sample was directly sieved to an electron microscope observation grid using a spoonful to obtain an observation sample. This sample has a random film thickness distribution depending on the size of the crystal grains. An electron beam focused at an acceleration voltage of 80 keV and a beam diameter of 0.7 nm is irradiated on a portion of the sample having a thickness of about 10 nm (this portion is determined by observation with an electron microscope), and an electron level is obtained. Transition information between them was obtained. As a measurement condition at this time, an adjustment was made such that there was no energy loss, that is, a half-value width of a so-called “zero loss peak” always achieved an energy resolution of 0.5 eV.

The EELS spectrum obtained in this way was compared with the analysis result 10 by an ultraviolet-visible spectrophotometer (UV-Vis), which is separately measured. The sample used in the UV-Vis analysis was prepared by using an Alq ₃ powder sample as an evaporation source and monitoring the film accurately on a quartz substrate with a film thickness monitor while maintaining a degree of vacuum of 2 × 10 ⁻⁴ Pa, an evaporation temperature of 160 ° C., and an evaporation rate of 0. Vapor deposition was performed under the condition of 0.05 nm / sec, and a film deposited to a thickness of 80 nm was used.

FIG. 2 shows the evaluation of the electron spectroscopic characteristics of an organic material sample in a powder state observed in an analysis region of 10 nm or less, and shows a transition process between π-π ^* electron energy levels related to molecular orbitals and ionization. It is a figure showing the result of the electron energy loss analysis which arises with a transition process. In the figure, 8 is the EELS spectrum actually obtained from the Alq ₃ powder sample, and 10 is the ultraviolet-visible spectrophotometer (UV-Vis) analysis result obtained from the Alq ₃ deposited film sample to be compared.
In the EELS spectrum 8 and the UV-Vis spectrum 10, spectra having maximums at 3.3, 4.7 and 6.4 eV, which correspond well to each other, were obtained.

All of these peaks are π → π ^* transition peaks, which correspond to the HOMO-LUMO band-to-band transition, the inter-band energy higher than the HOMO-LUMO band-to-band transition (eg, HOMO → LUMO + 1), and the ionization energy. (Details will be described with reference to FIG. 9).

A functional organic material such as Alq ₃ has a molecular orbital characteristic of a double bond or a cyclic structure called a π bond. In the example of FIG. 2, EELS generated by a plurality of transitions between electron levels from a π orbital, which is a binding molecular orbital occupied by an electron, to a π ^* orbital, which is an unoccupied antibonding molecular orbital having a higher energy. The state of the spectrum is confirmed.

This region is a part of the 0 to 30 eV loss energy region (Low-loss region) of the EELS spectrum 8 shown in FIG.
On the other hand, the molecular orbitals represented by π and π ^* are the HOMO level (the highest occupied molecular orbital) corresponding to the top of the valence band and the conduction orbit used when discussing the electronic behavior of organic materials. It has a correspondence with the LUMO level (lowest unoccupied molecular orbital) corresponding to the bottom of the body. For example, the lowest energy peak shown in FIG. 2 corresponds to the HOMO-LUMO transition.
This was made possible by observation in a nano-order analysis area.

  HOMO is the most reactive of the occupied orbitals occupied by electrons, while LUMO is the most reactive orbital of free orbitals. When an organic device represented by organic electroluminescence (organic EL) is constructed as an example of a structure containing an organic material, high injection efficiency of electrons and holes from an electrode to an organic layer is required. . For electron injection, organic molecules are required to have low LUMO values. On the other hand, the hole injection efficiency has a very high correlation with the HOMO value.

As described above, information relating to the molecular orbital that governs the electrical behavior of an organic material can be obtained with a positional resolution of 10 nm or less, which is a very effective means for evaluating an organic device.
Further, as compared with other methods such as the XPS method, a transition peak from the π orbit to the π ^* orbit is easily observed with high sensitivity. This is one of the advantages of the energy filter transmission electron microscope (EF-TEM).

(Evaluation method for simple elements containing organic materials)
As an example of the evaluation of the functional organic material, a simple device manufactured by the following procedure was used for the evaluation.
First, an Au electrode was laminated with a thickness of 50 nm on an acrylic plastic substrate. On top of this, Alq ₃ molecules 13 as a light emitting layer of an organic EL material were 50 nm, and subsequently, in an organic EL device, LiF12, which is famous as a cathode buffer layer, was heated at 570 ° C., a degree of vacuum of 2 × 10 ⁻⁴ Pa, and a deposition rate of 0. Vapor deposition was performed under the conditions of 0.1 nm / sec to obtain a cathode buffer layer having a thickness of 1 nm.
Further, Alq ₃ and LiF were alternately evaporated to 10 nm, 5 nm, 0.9 nm, and 0.7 nm, respectively, and finally Al14 was evaporated to a thickness of 50 nm. This element was cut with a cryomicrotome to a thickness of 30 nm and used as a sample. This sample was placed in an EF-TEM apparatus, and the electron beam focused at an acceleration voltage of 80 keV so that the beam diameter became 0.2 nm was continuously moved at a fixed position or at an analysis position at 0.4 nm intervals. EELS spectra were obtained.
In particular, in this simple device, analysis was performed in a region of 30 nm on the side of the Au electrode out of 1350 nm of Alq ₃ molecules, and it was found that a transition from a π orbital indicating a transition process between electron levels to a π ^* orbital having higher energy was performed. (Π → π ^* transition) was obtained as a spectrum having a maximum at 3.3, 4.7, and 6.4 eV. This value completely coincided with the separately performed UV-Vis spectrum.

(Evaluation of local charge state and charge distribution state of organic materials)
Next, measurement and evaluation of the local charge state of the organic material will be described. When electrons and holes, for example, are injected into a functional organic molecule, which is essentially a neutral molecule, by charge injection, it is useful information if an electronic structure spectrum corresponding to the charge state of the molecular structure can be observed. Accurately grasping the charge state of various organic materials will not only guide new material design, but also facilitate the prediction of characteristics and material deterioration in device fabrication. Give very useful information such as becoming.

  FIG. 3 is a schematic diagram showing a method for giving a charge to a sample in order to measure a local charge state or charge distribution state of an organic material. In this method, instead of actually fabricating a device into which charges are injected, such as an organic EL, and evaluating the charge state, charges can be simulated and charge can be simply evaluated.

In the figure, 11 indicates a Pt probe, 12 indicates lithium fluoride (LiF), and 13 indicates an Alq ₃ molecule as an organic material to be measured. The lithium fluoride 12 between the Pt probe 11 and Alq ₃ molecule 13 is intended to function as an agent of the action of lowering the injection barrier from the electron Pt probe 11 to Alq ₃ molecule 13.

On a Pt probe 11 for a scanning tunneling microscope having a tip diameter of about 10 nmφ, lithium fluoride (LiF) 12 used for a cathode buffer layer or the like of an organic EL device is vapor-deposited at an evaporation temperature of 570 ° C. and a vacuum degree of 570 ° C. Under a condition of 2 × 10 ⁻⁴ Pa and a deposition rate of 0.1 nm / sec, a film thickness of about 1 nm was laminated.
Next, while accurately monitoring the Alq ₃ molecules 13 with a film thickness monitor, the substrate temperature was set to −100 ° C., the degree of vacuum was 2 × 10 ⁻⁴ Pa, the deposition temperature was 160 ° C., and the deposition rate was 0.05 nm / sec. And deposited to a thickness of 10 nm. Thereafter, a heat treatment was performed for 30 minutes while maintaining the substrate temperature at 150 ° C.

Furthermore, LiF12 was again deposited thereon by vacuum evaporation under the conditions of an evaporation temperature of 570 ° C., a degree of vacuum of 2 × 10 ⁻⁴ Pa, and an evaporation rate of 0.1 nm / sec. By this treatment, a microstructure, which is an aggregate of several molecules of Alq ₃ molecules and surrounded by an extremely thin LiF layer, was formed near the tip of the ultrafine Pt probe 11. The Pt probe 11 with the Alq ₃ molecule 13 sandwiched between LiF 12 was introduced into the EF-TEM device so as to be fixed at a position horizontal to the observation grid for the electron microscope.

Subsequently, an electron beam focused on the tip of the Pt probe 11 at an acceleration voltage of 80 keV so that the beam diameter becomes 0.2 nm is continuously moved from the Pt probe 11 / LiF12 interface at an analysis position at an interval of 0.4 nm. Irradiated. At this time, the EELS spectrum was measured in the same manner as in FIG. 2 while confirming that the analysis was from the Alq ₃ molecules 13.

As a result, the EELS spectrum having the maximum around ₃ to 4 eV and 5 eV was obtained from the Alq ₃ molecule 13. The peak of 3 to 4 eV corresponds to an interband energy higher than the HOMO-LUMO interband transition (for example, HOMO → LUMO + 1, etc.), and the peak of 5 eV corresponds to the ionization energy. These peak positions are shown in the Alq ₃ powder sample shown in FIG. It was clearly different from the one. This is because, in the method of FIG. 3, the EELS spectrum corresponding to the charged Alq ₃ molecule to which electrons have been given was obtained because the minority molecular aggregate of Alq ₃ was covered with LiF.

For example, regarding the ionization energy, when comparing the neutral state and the charged state of the Alq ₃ molecule 13 confirmed in FIG. 2, the EELS spectrum of the charged state generated in the Alq ₃ molecule 13 due to the injection of electrons from LiF 12 is shown in FIG. By comparing the EELS spectra of the molecules in the neutral state shown in FIG. 2, information useful for organic molecular device design from the viewpoint of element structure, reliability, and the like can be obtained. For example, it has been pointed out that the deterioration of the organic EL element using the Alq ₃ molecule as a light emitting layer is related to the charge state accompanying the charge injection. By evaluating the state of charge related to the deterioration of these organic elements by the same method as described above, the deterioration mechanism can be clarified.

(Evaluation of local potential and local potential distribution of organic materials)
By paying attention to electron orbits such as HOMO and LUMO, and evaluating the transition energy with a positional resolution of several nm or less, a local potential or a potential distribution can be known.
For example, by knowing the energy of the electron transition (for example, HOMO-LUMO transition) of the organic material at the electrode interface, it is possible to know the difference in the potential distribution according to the combination of the electrode material and the organic material. Such information provides knowledge for controlling the injection efficiency of electrons and holes at the interface between materials, and can be used for constructing a device structure that has never been seen before.

FIG. 4 is a schematic diagram showing a local potential or a potential distribution derived from an EELS spectrum for one or a plurality of organic materials or a structure containing these organic materials.
In the figure, 14 is an Al electrode, 15 LiF12 / Alq ₃ 13 filling level at a distance from the interface (HOMO), 16 is LiF12 / Alq ₃ 13 empty level at a distance from the interface (LUMO), 17 LiF12 / Alq ₃ 13 empty level at a distance from the interface, 15 'LiF12 / Alq ₃ 13 filling level in the vicinity of the interface, 16' LiF12 / Alq ₃ 13 filling level in the vicinity of the interface, 17 'LiF12 / An empty level near the Alq ₃ 13 interface, 18 is a vacuum level on the Al electrode side, 18 ′ is an interface created by contacting dissimilar materials and a newly generated vacuum level, 19 is a work function of Al, 20 ionization potential of Alq _3, the transition peak 21 that is preferentially observed in places distant more than 20nm from LiF / Alq ₃ interface (6.0 eV), 22 is LiF / Alq ₃ field A transition peaks observed in close proximity (5.0 eV).

This will be described specifically with reference to FIG. An Al electrode 14 is formed to a thickness of 150 nm on a Si (111) substrate having a 300 nm SiO ₂ thermal oxide film by an electron beam evaporation method using a 100 μm wide line and space mask. The layers were stacked as follows. While accurately monitoring the Alq ₃ molecule 13 on the substrate with a film thickness monitor, the Alq ₃ molecule 13 is deposited under the conditions of a vacuum degree of 2 × 10 ⁻⁴ Pa, a deposition temperature of 160 ° C., and a deposition rate of 0.05 nm / sec. Then, LiF12 was laminated to a thickness of 1 nm under the conditions of an evaporation temperature of 570 ° C., a degree of vacuum of 2 × 10 ⁻⁴ Pa, and a deposition rate of 0.1 nm / sec.

A 100 μm-wide striped Al electrode 14 having a thickness of 150 nm was formed thereon as a cathode again by using a mask again. The sample thus produced was cut into a size of 10 μm in width, 5 μm in height, and 0.5 μm in thickness using an FIB apparatus.
As the processing conditions of FIB, Ga ions were accelerated at 30 keV under water-free conditions, and sputtering was performed from the sample surface. The current amount at the time of processing is controlled by the size of the drawing diameter. What was initially 20 nA was gradually reduced from 1000 nA to 1000 pA, 500 pA, 100 pA, 50 pA, 50 pA, 30 pA, and 10 pA at the same time as the thinning was advanced. Was. Finally, the sample was tilted by ± 1 degree, the accelerating voltage was reduced to 5 keV, and the surface was cleaned at 5 pA.
After embedding this exfoliated sample in epoxy resin, in order to perform further exfoliation under water-free conditions, the sample thickness was adjusted to 30 nm using a cryomicrotome, and the sample for analysis was used. did.

As shown in FIGS. 2 and 3, an electron beam focused on this sample at an acceleration voltage of 80 keV so that the beam diameter becomes 0.2 nm was continuously moved from the Al electrode 14 at an analysis position of 0.4 nm. The EELS spectrum was measured. FIG. 4 is a potential profile at the electrode interface created based on the results.
In the figure, 15, 16 and 17 away from LiF12 / Alq ₃ 13 interface, 15 ', 16', 17 'definitive closer to LiF12 / Alq ₃ 13 interface, the energy of the molecular orbitals in the mutual relationship Is schematically shown. Correspondence between the energy levels corresponding to these mutually are shown by the curve connecting each other, the curve shows how the potential profile is gradually curved toward LiF12 / Alq ₃ 13 interface.

Further, among 15, 16, 17, 15 ', 16' and 17 ', white squares indicate empty levels, and gray squares indicate full levels. Numeral 18 denotes a vacuum level as viewed from the Al electrode 14 side or from the Alq ₃ 13 side which is sufficiently far from the interface, and 18 ′ denotes a vacuum level near the Alq ₃ 13 side interface (where the Al electrode 14 and the LiF 12 It is known that the Al electrode 14 side and the Alq ₃ 13 side newly generated by the contact have a potential gradient of about 1.8 eV).

19 is a work function value, and the work function of the Al electrode 14 shows about 4.3 eV. Referring to FIG. 4, the energy level of Alq ₃ 13 at a position sufficiently distant from the interface will be described.
20 is the value of the ionization potential of Alq ₃ 13, the value of 5.7~6.6eV have been reported. Reference numeral 15 denotes the energy level of the HOMO of Alq ₃ 13, and reference numeral 16 denotes the energy level of the LUMO of the Alq ₃ 13 molecule. 15 'is the HOMO energy level at the interface the immediate vicinity of newly generated by LiF12 and Alq ₃ 13 are in contact.
21 is a transition peak observed preferentially at locations spaced above 20nm from LiF12 / Alq ₃ 13 interface, the values were generally indicates a value of about 6.0 eV. As described with reference to FIG. 2, this value corresponds to the ionization energy of 13 molecules of Alq ₃ in the neutral state.

In contrast, 22 represents a transition peaks observed preferentially at LiF12 / Alq ₃ 13 interface close proximity, the value showed about 5.0 eV. This value also corresponds to the ionization energy of 13 molecules of Alq ₃ in the charged state, as described in FIG. In the very vicinity of the LiF12 / Alq13 side interface, the vacuum level is reduced by about 1.8 eV and the HOMO is also reduced by about 0.5 eV, so that the ionization energy, which is the energy difference from HOMO to the vacuum level, is 5.0 eV. It is probable that a degree value was observed.
The difference of the peak positions found in two areas, a phenomenon observed in a structure in which different materials such LiF12 and Alq ₃ 13 are combined in close proximity, is caused by bending of the potential profile in the vicinity of the interface.

At a distance from the interface it does not undergo the electric influence of LiF12 layer, the energy loss peak of Alq ₃ 13 orphaned are most preferentially observed in response to the transition 21. On the other hand, in the vicinity of the LiF12 layer, a potential distribution is generated by the supply of electrons from the LiF12 layer, and a new filling level 16 'corresponding to the level 16 originally at the LUMO level is generated. This level is a level newly generated as a result of a small amount of electrification accumulating in the neutral LUMO level due to a charge less than one valence caused by partial occupation of electrons. It is distinguished from the HOMO level formed by two electrons having opposite spins, which is observed in the Alq13 molecule in the state. Similarly, a new filling level 15 'is generated for the level 15 which was originally at the HOMO level.

  As a result, when the electron beam is transmitted, an energy loss different from that of the transition 21 occurs due to the transition process 22. Through the observation, a local potential or a potential distribution near the interface is detected with a spatial resolution of several nanometers or less. can do.

(Confirmation of nano-order measurement using verification sample)
Next, in order to confirm the actual measurement resolution of an organic material, an example in which a standard sample for confirming nano-order measurement is created and verified will be described.
FIG. 5 shows a transition process between electron levels in an organic material and a local charge of the organic material with an electron beam irradiated at a vertical or finite angle with respect to the surface of the organic material with a spatial resolution of several nm or less. It is a figure which shows the example which evaluated the state and the local potential distribution of the organic material.
1 denotes an accelerated incident electron beam, 23 denotes copper phthalocyanine, and 24 denotes polyvinyl alcohol (PVA).

0.01 g of copper phthalocyanine 23 (formula 2) as a molecule to be dispersed is dissolved in 500 ml of a concentrated sulfuric acid solution.

On the other hand, a flask containing 1000 ml of polyvinyl alcohol (PVA) 24 (chemical formula 3) in an aqueous solution was cooled with ice water.

Thereto, 1 ml of the concentrated sulfuric acid solution mixed with the copper phthalocyanine 23 was mixed. By this treatment, microcrystalline particles of 1 to 10 molecules of copper phthalocyanine were generated in the PVA 24, and this sample was used as a dispersion model sample of functional molecules (standard sample for evaluation of measurement resolution).
This sample was sliced to a thickness of 30 nm with a cryomicrotome, placed on an observation grid for an electron microscope, and observed using an electron beam focused at an acceleration voltage of 120 keV so that the beam diameter became 0.2 nm. I got it.

A π → π ^* transition spectrum was obtained around 5.8 eV only from the region where copper phthalocyanine 23 was present. When an image was formed by dispersing only the energy loss of 5.8 eV and forming an image, the microcrystal in which copper phthalocyanine 23 was present was bright as a contrast, and only in the place where PVA was present, an image having a low contrast could be obtained.
The region where the copper phthalocyanine 23 was present had a dispersion of 1.5 to 15 nm, and was dispersed almost uniformly in the PVA 24. From these results, it was proved that the property evaluation of the organic material could be observed with a spatial resolution of 2 nm or less.

In addition, by evaluating each state of the material dispersed at the nano level, such as the dispersion model sample described above, the affinity between the materials can be evaluated.
In the case where the conductivity of a plastic film is to be improved by dispersing at least two or more materials, it is useful information to visualize the dispersion state of functional organic molecules that are effective for conductivity.

(Evaluation of cross section of organic multilayer structure)
Next, an example in which an evaluation is performed by irradiating an electron beam from a cross-sectional direction of a structure including a multilayer film including an organic material will be described.
FIG. 6 shows an electron beam irradiation from a direction (cross-sectional direction) perpendicular to the surface of a structure including an organic material, a transition process between electron levels, a local charge state of the organic material, and a local state of the organic material. FIG. 4 is a schematic diagram showing an example in which characteristic evaluation such as a potential distribution is performed with a spatial resolution of several nm or less.

In the figure, 1 is an accelerated incident electron beam, 12 is a LiF molecule, 13 is an Alq ₃ molecule, 14 is an Al electrode, 25 is a 300 nm SiO ₂ thermal oxide film, and 26 is a Si (111) substrate.
If the example introduced in FIG. 4 is further developed, the following can be understood. Similarly to FIG. 4, an Al electrode 14 was formed on a Si (111) substrate 26 provided with a 300 nm SiO ₂ thermal oxide film 25 by an electron beam evaporation method. The Al electrode 14 was stacked to a thickness of 150 nm using a mask made of 100 μm wide line and space.

On this substrate, Alq ₃ 13 was deposited under the conditions of a vacuum degree of 2 × 10 ⁻⁴ Pa, a deposition temperature of 160 ° C., and a deposition rate of 0.05 nm / sec while accurately monitoring with a film thickness monitor. Subsequently, LiF12 was laminated to a film thickness of 1 nm under the conditions of an evaporation temperature of 570 ° C., a degree of vacuum of 2 × 10 ⁻⁴ Pa, and a deposition rate of 0.1 nm / sec.
Again, while accurately monitoring Alq ₃ 13 with a film thickness monitor, vapor deposition was performed under the conditions of a vacuum degree of 2 × 10 ⁻⁴ Pa, a vapor deposition temperature of 160 ° C., and a vapor deposition rate of 0.05 nm / sec. Subsequently, LiF12 was laminated to a thickness of 3 nm under the conditions of an evaporation temperature of 570 ° C., a degree of vacuum of 2 × 10 ⁻⁴ Pa, and a deposition rate of 0.1 nm / sec.

A 100 μm-wide striped Al electrode 14 having a thickness of 150 nm was formed thereon as a cathode again by using a mask again. The sample prepared in this manner was cut into a size of 10 μm in width, 5 μm in height, and 0.5 μm in thickness using a FIB apparatus under water-free conditions.
As the processing conditions of FIB, Ga ions were accelerated at 30 keV, and sputtering was performed sequentially from the sample surface. The current amount at the time of processing is controlled by the size of the drawing diameter. What was initially 20 nA was gradually reduced from 1000 nA to 1000 pA, 500 pA, 100 pA, 50 pA, 50 pA, 30 pA, and 10 pA at the same time as the thinning was advanced. Was.

  Finally, the sample was tilted by ± 1 degree, the accelerating voltage was reduced to 5 keV, and the surface was cleaned at 5 pA. Then, after embedding the sliced sample in an epoxy resin, in order to perform further thinning treatment, the sample was cut by using a cryomicrotome so that a cross section could be observed at a sample thickness of 30 nm to obtain an analysis sample.

An electron beam focused on this sample at an accelerating voltage of 80 keV so that the beam diameter becomes 0.2 nm was analyzed by Alq ₃ 13 while continuously moving the analysis position from the upper Al electrode 14 at intervals of 0.4 nm. Was observed. As a result, a transition peak was observed mainly around 6.0 eV with good reproducibility. When these characteristics were evaluated, the spatial resolution was 1.5 nm or less.

(Interface evaluation of organic multilayer structure)
FIG. 7 shows an example in which the evaluation of the characteristic distribution at the interface between different materials and the vicinity thereof is performed with a spatial resolution of several nm or less in the structure including the organic material. In this example, the incident electrons accelerated in the sample configuration of FIG. 6 are made to enter the interface region.

That is, after embedding a sliced sample cut into a size of 10 μm in width, 5 μm in height, and 0.5 μm in thickness using an FIB apparatus in an epoxy resin, a cryomicrotome is used for further thinning treatment. The sample was cut so that a cross section could be observed with a sample thickness of 30 nm to obtain an analysis sample.
At an acceleration voltage of 80keV to this sample, the electron beam the beam diameter was converged to be 0.2 nm, while moving from the upper Al electrode 14 analyzes position continuously at 0.4nm intervals, LiF12 / Alq ₃ 13 interface The potential profile in the vicinity was observed.
As a result, it was observed that the potential was curved only in the vicinity of the respective Alq ₃ 13 interfaces from both the LiF having a thickness of 1 nm and the LiF having a thickness of 3 nm. At this time, the spatial resolution of the characteristic evaluation was 1.5 nm or less.

Note that the structure containing an organic material is not necessarily a laminated film, and may be a system in which two or more materials are dispersed. In any case, it was found that the characteristics based on the electronic structure at the interface and in the vicinity thereof were different from the characteristics in the isolated state.
For example, by analyzing characteristics such as an organic material / inorganic material interface and a transition process between electronic levels at an organic material / organic material interface for constructing an organic EL device, guidelines for material design and device design were obtained. .

(Difference in energy levels involved in electron or hole transport in the junction region)
FIG. 8 shows the evaluation of the difference in energy levels involved in the transport of electrons or holes in the junction region between different materials in a structure containing a plurality of organic materials at a spatial resolution of several nanometers or less. This is an example of a case where a device is manufactured based on the above. 23 indicates copper phthalocyanine, and 27 indicates polyvinyl carbazole containing carbon nanotubes.
For example, different organic materials are joined to produce an interface in which the shift amount of the HOMO energy position is within 0.5 to 3.0 eV. As a result, an organic device having a high-efficiency junction interface for achieving smooth hole movement, preventing excess holes from diffusing to the cathode side, and generating excitons with high efficiency with respect to input power is realized. Can be made.

  In these electronic devices, a comparative evaluation of an electron level involved in the transport of electrons or holes at an interface between different kinds of materials is made on the basis of an ionization potential and an interband energy higher than an HOMO-LUMO band transition (for example, HOMO). → LUMO + 1), HOMO-LUMO transition energy, and ionization potential or a known work function for metal materials.

Ａｌｑ₃１３、キナクリドン誘導体（化５）

混入Ａｌｑ₃膜、銅フタロシアニン２３、４，４’−ビス〔Ｎ−（１−ナフチル）−Ｎ−フェニルアミノ〕ビフェニル（化６）、

ポリデオキシチオフェン（PEDOT、化７）、

ポリチオフェン（化８）

等を各種接合して、電子デバイスとしての可能性を評価した。
その結果、イオン化エネルギーから導かれるＨＯＭＯエネルギー位置を近接する有機材料間で比較することにより、特に有機／有機接合界面での遷移エネルギーの差異は、０．５〜３．０ｅＶの範囲に収まることが好ましいことが明らかとなった。 Hereinafter, a specific example will be described. Polyvinyl carbazole (PVK) (Formula 4) as a polymer organic EL light emitting material,

Alq ₃ 13, a quinacridone derivative

Mixed Alq ₃ film, copper phthalocyanine 23, 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (formula 6),

Polydeoxythiophene (PEDOT, Chemical Formula 7),

Polythiophene (Chem. 8)

And the like were joined to evaluate the possibility as an electronic device.
As a result, by comparing the HOMO energy positions derived from the ionization energies between adjacent organic materials, the difference in the transition energies, particularly at the organic / organic junction interface, can be in the range of 0.5 to 3.0 eV. It turned out to be favorable.

  In addition, as a material other than the Al electrode 14, a high-concentration impurity is implanted into a noble metal such as Au or Ag, an oxide such as ITO, a halogen material such as LiF, a magnetic material such as Fe, or a semiconductor material such as Si. It is clear that the difference in transition energy at the organic material / inorganic material interface is preferably within the range of 0.5 to 3.0 eV, including those containing an alkaline material such as carbon, and Na. became.

For example, in the case where the carbon nanotube-containing PVK27 and copper phthalocyanine 23 shown in FIG. 8 are joined together, after developing PVK at a concentration of 5% by weight in a toluene solution, 0.3 g of carbon nanotubes are added, and an ultrasonic cleaner is used. And dispersed.
This sample was formed into a 70 nm thin film 27 with a spin coater under a rotation condition of 10,000 rpm. While accurately monitoring copper phthalocyanine 23 on the thin film with a film thickness monitor, the film was vapor-deposited under the conditions of a degree of vacuum of 2 × 10 ⁻⁴ Pa and a vapor deposition rate of 0.2 nm / sec to obtain a layer of 70 nm.

Thereafter, a Ca / Ag electrode was prepared on the PVK side, an ITO electrode was prepared on the copper phthalocyanine 23 side, and light was emitted at a luminance of 100 cd / m ^{2 when} an electric field of 5 V was applied.
On the other hand, a PVK film to which no carbon nanotubes were added and a copper phthalocyanine 23 film were joined to produce a Ca / Ag electrode on the PVK side, an ITO electrode was prepared on the copper phthalocyanine 23 side, and an electric field was continuously applied to 10 V, but light was emitted. Did not.

  These two types of samples were cut out into a size of 10 μm in width, 5 μm in height, and 0.5 μm in thickness using an FIB apparatus as in FIG. As the processing conditions of FIB, Ga ions were accelerated at 30 keV, and sputtering was performed from the sample surface. The amount of current at the time of processing is controlled by the size of the drawing diameter. What was initially 20 nA was gradually reduced from 1000 nA to 1000 pA, 500 pA, 100 pA, 50 pA, 50 pA, 30 pA and 10 pA at the same time as thinning was advanced. Was.

Finally, the sample was tilted by ± 1 degree, the acceleration voltage was reduced to 5 keV, and the surface was cleaned at 5 pA. After embedding this sliced sample in an epoxy resin, in order to perform further thinning treatment, the sample was cut using a cryomicrotome so that a cross section could be observed at a sample thickness of 30 nm to obtain an analysis sample. An EELS spectrum was obtained while an electron beam focused on the sample at an acceleration voltage of 80 keV such that the beam diameter became 0.2 nm was continuously moved from the upper Al electrode 14 at an analysis position of 0.4 nm. The difference in π → π ^* transition energy at this interface was 0.7 eV.

On the other hand, when the difference in π → π ^* transition energy at the interface in the non-light-emitting element was similarly evaluated, it was 0.1 eV.
Considering the peak observed in each measurement as the ionization energy of each material, if the energy gap at the interface is too small, the carriers flow into the counter electrode (if a hole, the cathode) and do not function as a light emitting device. I think that the.
As described above, it was possible to observe the characteristic evaluation of the structure containing the organic material with a spatial resolution of 2 nm or less.

(Comparison between electron energy loss data and molecular orbital calculation results)
Fig. 9 shows the measurement and analysis of the energy (energy loss) of electrons transmitted by irradiating an electron beam onto an organic material, performing calculations by the molecular orbital method, and comparing the measured and calculated values for material properties. 2 shows data from an organic material fine region analyzer that can perform the above method.
8 is the EELS spectrum used in FIG. 2, 9 is the calculation result of the molecular orbital method, 15 is the HOMO level, and 16 is the LUMO level.

The energy value of the transition process between electronic levels in each organic material that composes the sample is made to correspond to the quantum mechanical calculation value related to the molecular orbital of the organic material. By taking this into account, a comprehensive evaluation of the electronic structure of the material or structure can be made.
The molecular orbital calculation can be performed using the density functional theory method or the like, and the calculation function may be incorporated in a computer in the EF-TEM controller or may be calculated by a separate computer system.

Based on the energy value obtained by this calculation, the charge state, potential, etc. are evaluated according to the structure of the sample, etc., so that the energy diagram of the device structure when using each material is consistently shown, and the device development Has made it possible to design materials and devices with higher efficiency than ever before.
In order to correspond to the EELS spectrum of the neutral state (powder state) sample of the Alq ₃ molecule 13 shown in FIG. 2, the molecular structure corresponding to the minimum energy of the Alq ₃ molecule 13 is calculated by a density functional theory molecular orbital calculation program. I asked.

Next, an optical absorption spectrum calculation was performed on the Alq ₃ molecule 13 whose molecular structure was optimized in this way. At this time, the molecular orbitals before and after each transition were also calculated at the same time, and set in advance so that each could be visualized. In the density functional calculation, the HOMO-LUMO band gap energy tends to be underestimated, and thus a correction coefficient is included in advance.

After the calculation, the obtained spectrum and the three-dimensional shape of the electron cloud indicated by each molecular orbital were examined in detail, and it was determined whether the transition was a transition between π → π ^* electron energy levels.
The transition energy between the various molecular orbitals obtained in this manner is plotted on the horizontal axis and the transition oscillator strength is plotted on the vertical axis to make a graph 9, which is compared with the EELS spectrum 8 or the UV-Vis spectrum 10. went.
When the three types of transition peaks obtained in FIG. 2 are compared with the calculation results, the peaks at the calculation at 3.3, 4.7, and 6.4 eV also have a peak maximum, and a very good agreement with the measured data was confirmed. Was.

Further, with regard to the charged state shown in FIG. 3, similar calculations were performed for negatively charged Alq ₃ molecules, and the corresponding relationship was confirmed.
On the other hand, the samples with the potential distribution of FIG. 4, EELS spectra away from LiF12 / Alq ₃ 13 interface, whereas showed a value close to the transition energy calculated for approximately neutral molecule, near the interface is A shift to lower energy was indicated. This is because, due to the effect of the potential bending, a portion that was originally an empty level (LUMO) was partially filled to become a new filled level (HOMO). I got sex. As described above, the electronic structure formed by the organic material or the structure including the organic material can be effectively determined by comparing the observation data with the molecular orbital calculation.

(Effect of electron beam acceleration energy on EELS spectrum)
FIG. 10A is a schematic diagram showing that by controlling the acceleration energy of the electron beam used for the analysis, the transition energy between the electron energy levels is accurately obtained according to the composition, structure, and the like of the material. .
1 is an accelerated incident electron beam, 2 is an observation sample, in this case a crystalline powder sample of Alq ₃ molecules 13 having the same thickness of about 10 nm, and 8 shows an EELS spectrum actually obtained.

  The acceleration energy is set in the range of 5 to 1000 keV, and accordingly, the half-width of the zero loss peak or the loss peak associated with the inner-shell excitation inherent to various materials, for example, the 1S peak of carbon is set in the range of 0.02 to 3.0 eV. The electronic optical system is automatically adjusted so as to achieve the set half width. As a result, the detection of the signal peak of the measurement object is prevented from being hindered by, for example, the spread of the zero-loss peak, and the damage of the sample due to the electron beam is reduced. Can be evaluated for the transition energy between electron levels.

FIGS. 10B and 10C show EELS spectra obtained through a crystalline powder sample of Alq ₃ molecules 13 having the same thickness of about 10 nm when the acceleration voltage of incident electrons is set to 80 keV or 200 keV from the left. .
The spectroscope was adjusted so that the half-value widths of the zero loss peaks reached values of 0.5 eV and 0.7 eV, respectively. The energy resolution expressed by the half width of the zero loss peak was improved by lowering the acceleration voltage. On the other hand, the maximum intensity of the _zero- loss peak was defined as I _0, and the spread of energy at the base of the peak at a position of 1/100 of the intensity was measured. As a result, it was also accelerated to 2.7 and 4.8 eV. It was found that the voltage largely depends on the voltage.

The EELS spectra obtained at each acceleration voltage are compared. As already described with reference to FIG. 2, when an electron beam focused at an acceleration voltage of 80 keV and a beam diameter of 0.7 nm is irradiated to obtain an EELS spectrum, the EELS spectrum has a maximum at 3.3, 4.7, and 6.4 eV. 3 spectra were obtained.
On the other hand, when an EELS spectrum is obtained by irradiating an electron beam focused to an acceleration voltage of 200 keV and a beam diameter of 0.7 nm, a peak of 3.3 eV close to a zero loss peak is not observed, and the peak is 4.7 eV to 6.4 eV. Only two peaks with maxima were observed.

  In the analysis of the transition spectrum, since the discussion near the several eV near the zero loss peak is performed, it is more accurate to suppress the energy width at the foot of the zero loss peak, but the accuracy of the transition spectrum analysis is higher, but the acceleration voltage is higher than the image resolution of the electron microscope. In order to improve the performance, it is necessary to select an accelerating voltage according to each situation, for example, when the interface with the metal electrode or the organic material is strong against electron beams and contains many elements with heavy atomic numbers.

(Effect of heat)
FIG. 11 is a view for explaining a heating / cooling mechanism for adjusting the sample temperature when analyzing the transition energy.
In the figure, 28 is a single crystal thin film made of the above-described Alq ₃ molecule 13, 29 is a lattice sheet made of graphite, 30 is a tungsten sheet which can pass liquid helium for cooling and can be heated itself. Pipe.

  The lattice sheet 29 is used to efficiently transfer heat from the heating / cooling pipe to the sample, and the analysis is performed using an electron beam transmitted from between the lattices after passing through the sample. The intervals between the pipes are also set so as not to affect the analysis using the transmission electron beam. In this way, the EELS spectrum can be obtained while adjusting the heating and cooling of the sample.

Organic materials are known to take many forms due to their heating and cooling processes. Some devices using an organic material are required to have stable characteristics in a high-temperature environment, and thus need to be evaluated at a temperature different from normal temperature.
Further, as an additional effect by cooling the sample, an effect of avoiding electron beam damage to the organic material can be expected.
This method can be applied to materials other than organic materials, for example, by adjusting the temperature in the range of -270 ° C to 600 ° C for carbon-based materials, and -270 ° C to 1500 ° C for other materials. In addition, characteristics such as transition energy reflecting the thermal physical properties of each material can be continuously and accurately obtained.

The effect of heat will be specifically described using Alq ₃ molecules 13. The Alq ₃ molecule 13 has a melting point of 412 ° C., a glass transition temperature of 175 ° C., and crystallization temperatures of 328 ° C. and 200 ° C.
As for the sample, the degree of vacuum was 2 × 10 ⁻⁴ Pa and the deposition temperature was 160 ° C. while accurately monitoring the deposited film composed of the Alq ₃ molecules 13 on the grid for electron microscope sample observation with a film thickness monitor installed in a vacuum apparatus. A film having a thickness of 50 nm was deposited under the conditions of a deposition rate of 0.05 nm / sec.

  When a heat treatment is applied to this sample from room temperature, a region where crystallization occurs in the amorphous film is observed at around 175 ° C. When an electron beam focused on this sample at an acceleration voltage of 80 keV so as to have a beam diameter of 0.2 nm is observed as a transition spectrum by EELS analysis while continuously moving the analysis position at 1 nm intervals, a main peak of 6 is obtained. A strong spectrum began to be observed at an energy position of 4.7 eV and 3.3 eV in addition to 0.0 eV. Therefore, when only 4.7 eV loss energy was selected and imaging was performed, only the crystallized region was observed with a bright contrast, and the growth point of the crystal grain, that is, the nucleus generation point could be found.

By creating a nucleation point with good control based on these observations, an organic single crystal thin film can be formed. Then, it is conceivable to apply this technology to the production of Alq ₃ organic EL devices. For example, conventionally, thin films in an amorphous state have been used with an emphasis on ensuring reliability, and electrical characteristics have been sacrificed. However, use of a single crystal thin film can improve characteristics.
As described above, the present invention has been described, but the present invention is not limited to these examples unless it exceeds the gist.

FIG. 2 is a diagram illustrating a method for analyzing electron energy loss by an energy filter type electron microscope according to one embodiment of the present invention. The figure which shows the result of the electron energy loss analysis which accompanies the pi-pi ^* electronic energy level transition process, the ionization transition process, etc. regarding the molecular orbital of the organic material sample of a powder state. FIG. 3 is a schematic diagram showing a method for giving a charge to a sample in order to measure a local charge state. FIG. 4 is a schematic diagram illustrating a local potential distribution derived from an EELS spectrum for a structure including an organic material. The figure explaining the example which irradiates an electron beam with a perpendicular angle with respect to an organic material surface, and evaluates local charge state and potential distribution. FIG. 4 is a diagram illustrating an example of evaluating characteristics by irradiating an electron beam from a direction (sectional direction) perpendicular to the surface of a structure containing an organic material. FIG. 4 is a diagram illustrating an example of evaluating interface characteristics. FIG. 4 is a diagram illustrating an example of evaluating a difference in energy level involved in transport of electrons or holes in a junction region between different materials with a spatial resolution of several nanometers or less. The figure which compares the energy (energy loss) measurement result of the transmission electron with the calculation result by the molecular orbital method. The figure explaining the influence of electron beam acceleration energy. FIG. 3 is a diagram illustrating a heating / cooling mechanism for adjusting a sample temperature.

Explanation of reference numerals

1: incident electron beam 2: sample 3: heating and cooling system 4: analysis area 5: magnetic prism 6: electron beam 7: detector 8: electron beam energy loss (EELS) spectrum 9: calculation result of molecular orbital method

Claims (17)

  For a sample containing an organic material, the potential of the organic material in an analysis region that is about the same as or smaller than the size of a single molecule to be analyzed, or in an analysis region in which the diameter of a circumscribed circle is 0.01 nm to 10 nm. And at least one of a charge state and a charge state is evaluated.   An electron beam whose beam diameter is about the same as or smaller than the size of a single molecule of the molecule to be measured, or 0.01 nm to 10 nm is incident on a sample containing an organic material. A method for analyzing a fine region of an organic material, comprising: analyzing a fine region of the organic material based on electron energy loss data when a line passes through a sample.   The method for analyzing a fine region of an organic material according to claim 1 or 2, wherein the sample is in the form of a flake cut out under a water-inhibited condition by a FIB and / or a cryomicrotome.   4. The method for analyzing a fine region of an organic material according to claim 3, wherein the sample is cut out by FIB, and a damaged portion generated on the cut surface is further cut out by a cryomicrotome.   3. The method for analyzing a fine region of an organic material according to claim 1, wherein the thickness of the flake shape is 1 nm to 300 nm.   3. The method for analyzing a fine region of an organic material according to claim 1, wherein the sample has a structure in which two or more different materials including an organic material are stacked, and the sample is cut in a direction in which a stacked cross section of the sample appears.   3. The method according to claim 1, wherein the sample is an organic EL device or an organic semiconductor device.   3. The method according to claim 1, wherein the data relating to the electron energy loss is obtained by an energy filter type electron microscope. The method according to claim 1, wherein the data relating to the electron energy loss is electron energy loss data generated during a π-π ^* electron energy level transition process or an ionization transition process, which is related to a molecular orbital of the organic material. 3. The method for analyzing a fine region of an organic material according to item 2.   The method according to claim 1 or 2, wherein the analysis performed based on the data regarding electron energy loss is an analysis of a local charge state or a charge distribution state.   3. The method for analyzing a fine region of an organic material according to claim 1, wherein the analysis performed based on the data regarding the electron energy loss is an analysis of a local potential or a potential distribution of the organic material.   3. The method according to claim 1, wherein the analysis performed based on the data regarding the electron energy loss is an analysis of an interface between the organic material and another material adjacent thereto and a characteristic distribution in the vicinity of the interface. A method for analyzing a fine region of an organic material according to the above.   The analysis performed based on the data regarding electron energy loss is an analysis of a difference in an energy level involved in transport of electrons or holes in a junction region between different materials including an organic material. 3. The method for analyzing a fine region according to 1 or 2. A sample mounting portion for mounting a sample containing an organic material,
An electron beam irradiation mechanism for injecting an electron beam having a beam diameter of 0.01 nm to 10 nm into the sample,
An organic material fine region analysis apparatus, comprising: an electron energy loss detection unit that acquires electron energy loss data when the electron beam passes through a sample.   By adjusting the acceleration energy of the electron beam in the range of 5 to 1000 keV, the half width of the energy loss peak caused by the transmission of the electron beam through the sample is controlled to be in the range of 0.02 eV to 3.0 eV. The apparatus according to claim 14, wherein a transition energy value according to the sample is determined.   The organic material fine area analysis apparatus according to claim 14, further comprising a sample heating / cooling mechanism.   The organic material fine evaluation area analyzer according to claim 14, further comprising a molecular orbital method calculation function.

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